York DH 240 Installation Manual download pdf (Page 56)

129963-YIM-A-0605

56 Unitary Products Group

8. If 24 volts is present at the UCB Y2 terminal, the

compressor may be out due to an open high-pres-

sure switch, low-pressure switch, or freezestat.

Check for 24 volts at the HPS2, LPS2, and FS2

terminals of the UCB. If a switch has opened, there

should be a voltage potential between the UCB ter-

minals, e.g. if LPS2 has opened, there will be 24

volts of potential between the LPS2 terminals.

9. If 24 volts is present at the UCB Y2 terminal and

none of the protection switches have opened, the

UCB may have locked out the compressor for

repeat trips. The UCB should be flashing a code. If

not, press and release the ALARMS button on the

UCB. The UCB will flash the last five alarms on the

LED. If the compressor is locked out, remove any

call for cooling at the thermostat or by disconnect-

ing the thermostat wiring at the Y2 UCB terminal.

This will reset any compressor lock outs.

NOTE: While the above step will reset any lock outs,

compressor #1 will be held off for the ASCD,

and compressor #2 may be held off for a por-

tion of the ASCD. See the next step.

10. If 24 volts is present at the UCB Y2 terminal and

none of the switches are open and the compressor

is not locked out, the UCB may have the compres-

sor in an ASCD. Check the LED for an indication of

an ASCD cycle. The ASCD should time out within

5 minutes. Press and release the TEST button to

reset all ASCDs.

11. The UCB can be programmed to lock out compres-

sor operation during free cooling and in low ambi-

ent conditions. These options are not enabled by

default. Local distributors can test the UCB for this

programming.

12. If none of the above corrected the error, test the

integrity of the UGB. Disconnect the C2 terminal

wire and jumper it to the Y2 terminal. DO NOT

jump the Y2 to C2 terminals. If the compressor

engages, the UCB has faulted.

13. If none of the above correct the error, replace the

UCB.

On a call for cooling, the supply air blower motor and

compressor #2 are operating but compressor #1 is not

(the room thermostat fan switch is in the “AUTO” posi-

tion).

1. Compressor #2 is energized in place of compres-

sor #1 when compressor #1 is unavailable for cool-

ing calls. Check the UCB for alarms indicating that

compressor #1 is locked out. Press and release

the ALARMS button if the LED is not flashing an

alarm.

2. Check for line voltage at the compressor contactor,

M1, and that the contactor is pulled in. Check for

loose wiring between the contactor and the com-

pressor.

3. If M1 is pulled in and voltage is supplied at M1,

lightly touch the compressor housing. If it is hot, the

compressor may be off on inherent protection.

Cancel any calls for cooling and wait for the inter-

nal overload to reset. Test again when cool.

4. If M1 is not pulled in, check for 24 volts at the M1

coil. If 24 volts is present and M1 is not pulled in,

replace the contactor.

5. Failing the above, if voltage is supplied at M1, M1

is pulled in, and the compressor still does not oper-

ate, replace the compressor.

6. If 24 volts is not present at M1, check for 24 volts at

the UCB terminal, C1. If 24 volts is present, check

for loose wiring between C1 and the compressor

contactor.

7. If 24 volts is not present at the C1 terminal, check

for 24 volts from the room thermostat at the UCB

Y1 terminal. If 24 volts are not present at the UCB

Y1 terminal, the UCB may have faulted. Check for

24 volts at the Y1 ECON terminal. If 24 volts is not

present at Y1 “ECON”, the UCB has faulted. The

UCB should de-energize all compressors on a loss

of call for the first stage of cooling, i.e. a loss if 24

volts at the Y1 terminal.

8. If 24 volts are present at the UCB Y1 terminal, the

compressor may be out due to an open high-pres-

sure switch, low-pressure switch, or freezestat.

Check for 24 volts at the HPS1, LPS1, and FS1

terminals of the UCB. If a switch has opened, there

should be a voltage potential between the UCB ter-

minals, e.g. if LPS1 has opened, there will be a 24-

volt potential between the LPS1 terminals.

9. If 24 volts is present at the UCB Y1 terminal and

none of the protection switches have opened, the

UCB may have locked out the compressor for

repeat trips. The UCB should be flashing a code. If

not, press and release the ALARMS button on the

UCB. The UCB will flash the last five alarms on the

LED. If the compressor is locked out, remove any

call for cooling. This will reset any compressor lock

outs.

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York DH 240 Installation Manual Page 56

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